Snowmobile having a parallel-path exhaust system for two-stroke engine

ABSTRACT

A snowmobile includes a frame, at least one ski, handbars operatively coupled to the at least one ski, and an engine assembly comprising an engine and an exhaust manifold. The exhaust manifold includes at least a first inlet, a first outlet, and a second outlet. The first inlet is configured to connect to a first exhaust port. The first outlet is connected to provide exhaust received from the first inlet to a first exhaust path and the second outlet is connected to provide exhaust received from the first inlet to a second exhaust path.

CROSS-REFERENCE TO RELATED TO APPLICATION(S)

This application is a continuation-in-part of U.S. application Ser. No.16/103,718, filed Aug. 14, 2018 and titled “PRESSURIZED OIL SYSTEMPOWERED BY TWO-STROKE ENGINE”, which claims the benefit of U.S.Provisional Application No. 62/545,824, filed on Aug. 15, 2017, both ofwhich are incorporated herein by reference herein. A claim of priorityis made.

TECHNICAL FIELD

This invention relates generally to exhaust systems, and in particularto exhaust systems utilized in conjunction with turbocharged two-strokeengines.

BACKGROUND

Two-stroke engines are commonly employed in recreational vehicles, suchas snow vehicles, due to the simplicity of design, power, and efficiencyas compared with four-stroke engines. Turbochargers may be utilized inconjunction with a two-stroke engine to increase power. A turbochargerutilizes a turbine to extract energy from the exhaust of the two-strokeengine. The extracted energy drives a compressor, which providescompressed air to the engine for combustion. The provision of compressedair to the two-stroke engine increases the amount of fuel that iscombusted, and therefore increases the power generated by the two-strokeengine. There remains a need to improve the efficacy and responsivenessof two-stroke engines employing turbochargers, particularly in thecontext of snow vehicles and snowmobiles.

SUMMARY

In order to improve responsiveness, it has been determined that it wouldbe beneficial to locate the turbocharger relatively close to the exhaustoutlet of the two-stroke engine and, in some instances, in a parallelarrangement with an expansion chamber. In some embodiments, an exhaustmanifold includes at least a first inlet and a first and second outlet.The first inlet is configured to connect to at least a first exhaustport. The first outlet is connected to provide exhaust received from thefirst inlet to a first exhaust path. The second outlet is connected toprovide exhaust received from the first inlet to a second exhaust path.

In some embodiments, a snowmobile a frame, at least one ski, handlebarsoperatively coupled to the at least one ski, and an exhaust system,which includes an exhaust manifold, an expansion chamber, and aturbocharger. The exhaust manifold includes first and second inlets andfirst and second outlets, wherein the first inlet is connected toreceive exhaust from a first cylinder and the second inlet is connectedto receive exhaust from a second cylinder. Exhaust provided at the firstand second inlets is communicated by the exhaust manifold to the firstand second outlets. The expansion chamber is connected to receiveexhaust from the first outlet. The turbocharger is connected to receiveexhaust from the second outlet.

In some embodiments, a snowmobile includes an engine system, wherein theengine system includes a two-stroke engine, an expansion chamber, aturbocharger, an exhaust muffler, and an intake manifold. The two-strokeengine includes at least a first combustion cylinder. The exhaustmanifold includes at least a first inlet and first and second outlets,wherein the first inlet is connected to receive exhaust from the firstcombustion cylinder. Exhaust provided at the first inlet is communicatedby the exhaust manifold to the first and second outlets. The expansionchamber is connected to receive exhaust from the first outlet and theturbocharger is connected to the second outlet to receive exhaust fromthe second outlet. Turbocharger utilizes the received exhaust togenerated compressed air at a compressed air outlet. The exhaust muffleris connected to receive exhaust output from the turbocharger and anintake manifold is connected to receive compressed air from theturbocharger and to provide the compressed air to the first combustioncylinder for combustion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a snow vehicle according to one embodiment.

FIG. 2 is a block diagram of an oil distribution system that includes afirst total-loss oiling system and a closed-loop oiling system accordingto one embodiment.

FIG. 3 is a perspective view of a two-stroke engine and oil pumputilized in the closed-loop oiling system according to one embodiment.

FIG. 4 is a perspective view of a two-stroke engine and exploded view ofthe oil pump utilized in the closed-loop oiling system according to oneembodiment.

FIG. 5 is a perspective view of a two-stroke engine and exploded view ofthe oil pump and oil tank according to one embodiment.

FIG. 6 is a perspective view of a two-stroke engine and installed oiltank according to one embodiment.

FIG. 7 is an exploded rear view of the oil pump according to oneembodiment.

FIG. 8 is an exploded front view of the oil pump according to oneembodiment.

FIG. 9 is an exploded view of the oil pump mechanically coupled to thecrankshaft according to one embodiment.

FIG. 10 is a perspective view of a two-stroke engine including anaccessory connected to receive oil from the closed-loop oiling systemaccording to one embodiment.

FIGS. 11A-11B are side views of a snow vehicle including a turbochargeraccording to one embodiment.

FIG. 12 is a perspective view of a two-stroke engine including aturbocharger connected to receive oil from the closed-loop oiling systemaccording to one embodiment.

FIGS. 13A and 13B are perspective views of a turbocharger according toone embodiment.

FIGS. 14A-14D are perspective views of a cooling circuit utilized inconjunction with a turbocharger and charge air cooler according to oneembodiment.

FIG. 15 is a perspective view of a two-stroke engine including a pair ofoil pumps configured in a stacked configuration according to oneembodiment.

FIG. 16A-16F are block diagrams of a closed-loop oiling system accordingto various embodiments.

FIGS. 17A-17D are block diagrams of the two-stroke engine and parallelpath exhaust system according to some embodiments.

FIGS. 18A-18D show various views of a parallel path exhaust systemutilized in conjunction with a two-stroke engine and turbochargeraccording to some embodiments.

FIGS. 19A-19B are perspective and exploded views, respectively, of aparallel path exhaust system with two-stroke engine removed for clarityaccording to some embodiments.

FIGS. 20A-20B are perspective and exploded views, respectively, of theparallel path exhaust system with charge air cooler and exhaust mufflerremoved for clarity according to some embodiments.

FIGS. 21A-21C are perspective, side, and top views, respectively, of theparallel path exhaust system utilized in conjunction with a two-strokeengine and turbocharger according to some embodiments.

FIGS. 22A-22C show various views of a parallel-path exhaust system withtwo-stroke engine, charge air cooler, and exhaust muffler removed forclarity according to some embodiments.

FIG. 23 is a perspective view of an exhaust muffler according to someembodiments.

FIGS. 24A-24D are perspective, top, side, and front views of an exhaustmanifold utilized to bifurcate the exhaust into first and second pathsfor the parallel path exhaust system according to various embodiments.

FIGS. 25A-25D are top, perspective, side, and front views of an exhaustmanifold utilized to bifurcate the exhaust into first and second pathsfor the parallel path exhaust system according to various embodiments.

FIGS. 26A-26D are top, perspective, side, and front views of an exhaustmanifold utilized to bifurcate the exhaust into first and second pathsfor the parallel path exhaust system according to various embodiments.

FIGS. 27A-27D are top, perspective, side, and front views of an exhaustmanifold utilized to bifurcate the exhaust into first and second pathsfor the parallel path exhaust system according to various embodiments.

FIGS. 28A and 28B are perspective and exploded views, respectively, of aparallel path exhaust system, with the two-stroke engine removed in FIG.28B for clarity according to some embodiments.

FIG. 29 is an exploded view of a parallel path exhaust system utilizingboth an internal wastegate and an external wastegate according to someembodiments.

FIG. 30 is a perspective view of a tuned expansion chamber with a fixedflow orifice according to some embodiments.

DETAILED DESCRIPTION

Referring to FIG. 1, a side view of a snow vehicle 10 is illustrated. Inthis embodiment, snow vehicle 10 is a snowmobile that includes track 12,seat 14, one or more skis 16, hood 18, handlebars 20 and engine 22(obscured by hood 18). As discussed in more detail below, engine 22includes a first oiling system and a second oiling system. In someembodiments, the first oiling system is a total loss oiling systemutilized to lubricate engine 22. In some embodiments, the second oilingsystem is a pressurized, closed-loop oiling system utilized to providelubrication to one or more accessories, which may be associated withengine 22. The second oiling system includes at least one pump,mechanically coupled to the engine 22 to provide the desired oilpressure—typically greater than that provided in the first oilingsystem. Utilizing a second oiling system, distinct from the first oilingsystem, allows engine 22 to make use of one or more accessories—such asturbocharger(s)—utilizing higher oil pressure than the available in thetwo-stroke engine relying on a total loss oiling system.

Referring now to FIG. 2, a block diagram of an oil distribution system28 is shown that includes a first oiling system 30 and a second oilingsystem 32. In the embodiment shown in FIG. 2, first oiling system 30includes first oil tank 34, first oil pump 36, two-stroke engine 22, andexhaust 40. Second oiling system 32 comprises second oil tank 42, secondoil pump 44, filter (optional) 46, pressure regulator 48 and accessory50. In this embodiment, first oiling system 30 is a total-loss system,in which oil provided to lubricate components of engine 22 is eventuallycombusted and dispelled into the atmosphere via exhaust 40. Inparticular, oil stored in first oil tank 34 is provided by one or moreoil pumps 36 to two-stroke engine 22. The oil provided by oil pump(s) 36is relatively low-pressure, which may be mixed with fuel and/or air andintroduced in the cylinder(s), in the crankcase, or in both thecylinders and the crankcase. Oil provided by first oiling system 30 maybe inadequate to properly lubricate one or more other accessories, suchas a turbocharger.

In order to provide oil at a relatively higher oil pressure than that ofthe total-loss oiling system, a second oiling system 32 is provided. Insome embodiments, the second oiling system 32 provides oil at a flowrate and/or pressure higher than that of the first oiling system 30. Oilpressure in the second oiling system 32 is developed by pump 44, whichis mechanically coupled to the engine 22. In this way, although engine22 is lubricated using a traditional total-loss oiling system,mechanical power provided by the engine is utilized to develop the oilpressure necessary for lubricating one or more accessories 50, such asone or more turbochargers and/or a high-pressure direct injection (HPDI)pressure pump assembly. In some embodiments, the second oiling system 32provides oil to lubricate a cam lobe of an HPDI pressure pump assembly.

In the embodiment shown in FIG. 2, pump 44 is mechanically coupled toengine 22, and more particularly to the crankshaft (not shown in thisview) of engine 22. Mechanical power generated by two-stroke engine 22is utilized to drive pump 44. In contrast with the first oiling system30, which provides oil at relatively low pressures to two-stroke engine22 (e.g., less than 10 pounds per square inch (PSI)), the mechanicalcoupling of pump 44 to two-stroke engine 22 allows oil provided by pump44 to be provided at higher pressures (e.g., greater than 10 PSI). Insome embodiments, pressurized oil is filtered by filter 46 and regulatedto a desired pressure by pressure regulator 48, wherein oil may bereturned to second oil tank 42 from pressure regulator 48 if thepressure exceeds a desired pressure. As discussed below, someembodiments the respective locations of filter 46 and pressure regulator48 may be modified—for example, by placing the pressure regulator 48upstream of filter 46. Pressurized oil is fluidly communicated to one ormore accessories 50 to lubricate the one or more accessories. In someembodiments, either in conjunction with or independent of utilizing thepressurized oil provided by second oiling system 32 for lubrication, thepressurized oil is utilized to provide hydraulic power to one or morecomponents, and the oil is then returned to second oil tank 42. In someembodiments, oil provided to accessory 50 returns to second oil tank 42simply due to gravity. In other embodiments, a secondary pump or 2 stagepump assembly (e.g., scavenge pump) may be utilized to pump oil utilizedby accessory 50 to second oil tank 42. As described below (for example,with respect to FIG. 13), the scavenge pump may similarly bemechanically coupled to the engine 22, such that mechanical powergenerated by the two-stroke engine 22 is utilized to drive the scavengepump. In some embodiments, one or both of the oiling systems (firstoiling system 30 and second oiling system 32) includes an oil cooler tocool the oil.

The oil pressure provided by second oiling system 32 to accessory 50 mayvary in some embodiments based on the engine RPM and/or engine load. Insome embodiments, pressurized oil provided to accessory 50—under mostoperating conditions—has a pressure greater than that provided by firstoiling system 30. In some embodiments, pressurized oil provided toaccessory 50 may vary based on engine RPMs and/or engine load, but whilethe engine is running will provide an oil pressure that exceeds 10 PSIand, in some embodiments exceeding 20 PSI, 30 PSI, or 40 PSI. In someembodiments, the oil pressure generated by pump 44 and/or regulated bypressure regulator 48 is selected to satisfy the particular requirementsof accessory 50. For example, in embodiments in which accessory 50 is aturbocharger, pressure provided may be greater than 10 PSI, 20 PSI, 30PSI, and, in some embodiments, greater than 40 PSI. In this way, thesecond oiling system provides pressurized oil to one or moreaccessories. One of the benefits of this arrangement, in addition to thehigher pressure provided by the second oiling system 32, is the abilityto utilize oil in the second oil tank 42 having a composition selectedspecifically for lubricating the one or more accessories. That is,because oil utilized in first oiling system 30 is separate from the oilutilized in second oiling system 32, each can utilize a type of oilselected specifically for the particular application (e.g., first oiltank 34 may be comprised of oil selected to lubricate a two-strokeengine 22, while second oil tank 42 may be comprised of oil selected tolubricate the attached accessory 50). In some embodiments, the oilselected to lubricate the two-stroke engine 22 has a first viscosity orfirst range of viscosities, for example if it is a multi-viscosity oil.And, in some embodiments, the oil selected to lubricate (or power) theattached accessory 50 may have a second viscosity or second range ofviscosities, for example if it is multi-viscosity oil. In someembodiments, the first viscosity (or first range of viscosities) isdifferent than the second viscosity (or second range of viscosities).Further, in some embodiments, the oil selected to lubricate thetwo-stroke engine 22 may have different additives than the oil selectedto lubricate (or power) the attached accessory 50. In some embodiments,first oil tank 34 and/or second oil tank 42 are closed, but in otherembodiments, first oil tank 34 and/or second oil tank 42 are vented.

Referring now to FIGS. 3-6, perspective views of a two-stroke engine 22are shown that include the oil pump 44 utilized in the second oilingsystem described with respect to FIG. 2. In particular, FIG. 3illustrates oil pump 44 in an assembled and installed state; FIG. 4illustrates oil pump 44 in an exploded view that illustrates componentsof an embodiment of an oil pump 44; FIG. 5 illustrates oil pump 44 andan embodiment of an oil tank 42 in an exploded view; and FIG. 6illustrates an embodiment of an oil pump 44 (not visible) and oil tank42 in an assembled state.

The embodiments shown in FIGS. 3-6 illustrates a two-cylinder,two-stroke engine, which may or may not include exhaust valve assemblies54 a and 54 b (in some embodiments), exhaust ports 56 a and 56 b, airintake ports 58 a and 58 b, crankshaft 60, oil inlet ports 62, 64 a and64 b associated with the first oiling system 30 (i.e., the total lossoiling system associated with two-stroke engine), and fuel inlet port66. In some embodiments, fuel is provided to a fuel rail via fuel inletport 66. First oiling system 30 provides lubrication to engine 22. Inparticular, oil is mixed directly with fuel via oil inlet port 62, andin addition is distributed into the crankcase via oil inlet ports 64 aand 64 b. As discussed above, in at least some embodiments, oil providedby the first oiling system to oil inlet ports 62, 64 a, and 64 b isprovided at a relatively low pressure, and may therefore not be at ahigh enough pressure for accessories (not shown in this view) thatrequire a higher oil pressure. In some embodiments, oil provided by thefirst oiling system to oil inlet ports 62, 64 a, and 64 b is provided atpressures less than 10 psi. In the embodiment shown in FIG. 3, thesecond oiling system 32, which in particular includes oil pump 44 andassociated inlet/outlet ports 68 a and 68 b, operates a pressure greaterthan the first oiling system.

In the embodiment shown in FIG. 3, oil pump 44 is mechanically coupledto crankshaft 60. In this way, mechanical power developed in crankshaft60 is delivered to oil pump 44, which provides pressurized oil to one ormore accessories (not shown in this view). As described above, oil inletports 62, 64 a and 64 b are configured to provide oil to the cylindersand crankcase as part of the two-stroke oiling system (i.e., firstoiling system 30), and are therefore not in fluid connection with oilpump 44. That is, as described with respect to FIG. 2, two distinctoiling systems are included: the two-stroke oiling system utilized tolubricate engine components such as the cylinders and crankcase as partof a total loss oiling system, and the pressurized accessory oilingsystem utilized to provide pressurized oil to one or more accessories.As illustrated in FIG. 3, some benefits of second oiling system 32 are:ability to provide pressurized oil in a limited amount of space (i.e.,does not take up much real estate within engine 22); ability to provideoiling systems at different pressures; ability to provide oiling systemswith different oils.

FIG. 4 is a perspective view of a two-stroke engine 22 and exploded viewof oil pump 44 utilized in the second oiling system 32 according to oneembodiment. In the embodiment shown in FIG. 4, oil pump 44 is a gerotorpump that includes mount 70, o-ring 72, bushing 74, shaft extender 76,gerotor housing 78, gear pair 80, inlet/outlet plate 82, inlet/outletfitting 84, bolts 86 a and 86 b, and inlet/outlet port 68 a and 68 b.

In this embodiment, oil pump 44 is bolted to mount 70 using one or morefasteners such as bolts 86 a and 86 b. A shaft 88 (partially visible) ismechanically coupled to crankshaft 60 to deliver mechanical power fromcrankshaft 60 to oil pump 44 (e.g., via a power take-off). Rotatingshaft 88 is surrounded, at least in part, by bushing 74. In otherembodiments, bushing 74 is replaced by a sealed bearing assembly thatsurrounds rotating shaft 88. Shaft extender 76 is coupled to shaft 88,which in turn is coupled to the gear pair 80 housed within gerotorhousing 78. Mechanical power causes one of the gerotor gears to rotaterelative to the other gear, which results in fluid (e.g., oil) beingpumped from an inlet/outlet port 68 a, through inlet/outlet plate 82, tothe other inlet/outlet port 68 b. Mechanical power delivered to thegerotor ring (e.g., inner ring) results in oil being pumped from one ofthe inlet/outlet ports 68 a to the other inlet/outlet port 68 b.

FIG. 5 is a perspective view of a two-stroke engine 22 and exploded viewof the assembled oil pump 44 and oil tank 42 according to oneembodiment. One of the inlet/outlet ports 68 a and 68 b is positioned todraw oil from oil tank 42. As a closed-loop system, oil drawn from oiltank 42 by oil pump 44 is provided to one or more accessories and thenreturned to oil tank 42 as part of a recirculation path.

FIG. 6 shows a perspective view of an embodiment of a two-stroke engine22 having an oil tank 42 installed. By locating oil pump 44 near thebottom of the engine, in at least some embodiments, oil is returned tooil tank 42 via gravity, without requiring a separate scavenge pump.However, it should be noted that in some embodiments, the location ofoil pump 44 and oil tank 42 may be located in an appropriate location orconfiguration.

Referring now to FIGS. 7, 8, and 9, exploded views of an embodiment ofoil pump 44 are provided. In particular, FIGS. 7 and 8 illustrateexploded views of oil pump 44, and FIG. 9 illustrates an exploded viewof oil pump 44, which is mechanically coupled with crankshaft 60according to various embodiments. As discussed with respect to FIG. 4,oil pump 44 includes o-ring 72, bushing 74, oil seal 75, shaft extender76, gerotor housing 78, gear pair 80, inlet/outlet plate 82,inlet/outlet fitting 84 and inlet/outlet ports 68 a and 68 b. FIGS. 7and 8 illustrate the power take-off shaft 88 and gearing utilized totransfer mechanical power from crankshaft 60 to oil pump 44. Theembodiment shown in FIGS. 7 and 8, power take-off shaft 88 includesfirst portion 90, second portion 92 and gear 94. In some embodiments,gear 94 is a helical gear or spur gear that is coupled to the gear 112(shown in FIG. 9) of crankshaft 60 in a crossed configuration in orderto communicate mechanical power from a first axis to a perpendicularaxis. In one embodiment, first oiling system 30 provides oil tolubricate the gear 112 (e.g., worm gear), wherein provided oil isreturned to oil first oil tank 34 (shown in FIG. 2) and eventuallyprovided to inlet ports 62, 64 a and 64 b, as part of the total lossoiling system.

The first portion 90 of power-take-off shaft 88 is housed and, in someembodiments, at least partially supported via bushing 74. As discussedabove, in some embodiments the bushing 74 may be replaced with a sealedbearing assembly (e.g., roller bearing or ball bearing). First portion90 is coupled to shaft extender 76, which in turn is mechanicallycoupled or integral in some embodiments to inner gear 102 of the gearpair 80. In this way, mechanical energy developed by the engine 22 incrankshaft 60 is communicated to inner gear 102. As inner gear 102rotates relative to outer gear 100, the difference in number of teethbetween inner gear 102 and outer gear 100 results in oil being drawninto the gears from a suction port (e.g., either inlet/outlet port 68 aor 68 b) and expelled through a discharge port (e.g., inlet/outlet port68 a or 68 b). In some embodiments, the rotational speed of the shaftdetermines, at least in part, the volume, flow rate, and/or pressure ofthe oil expelled through the discharge port. As the shaft speedincreases, the volume, flow rate, and/or pressure of oil dischargedincreases. In other embodiments, the pressure, flow rate, and/or volumeof oil discharged is further calibrated by alternate widths of innergear 102 and outer gear 100. In some embodiments, a pressure regulatoris utilized in conjunction with the oil pump 44 to limit/regulate theoil pressure provided. In some embodiments, the pressure regulator maybe incorporated as part of oil pump 44, while in other embodiments thepressure regulator may be implemented external to oil pump 44, forexample downstream of the oil pump 44. In some embodiments, the oil pump44 is a variable flow pump, for example a gerotor variable flow pump.

FIG. 9 illustrates the interaction between gear 94 and crankshaft 60. Inparticular, FIG. 9 illustrates connecting rods 110 a and 110 b, whichare connected at a distal end to respective pistons (not shown), forexample via wrist pins (also not shown), and on the other end tocrankshaft 60. Although shown in FIG. 9 in relation to a two-cylinderengine, engines of any number of cylinders can be employed. Thereciprocating motion provided by the pistons and connecting rods 110 aand 110 b causes crankshaft 60 to rotate about an axis y. In theembodiment shown in FIG. 9, crankshaft 60 includes gear 112, locatedbetween connecting rods 110 a and 110 b (and further located between oilseals 114 a and 114 b). Gear 112 is configured to interact with gear 94,causing power take-off shaft 88 to rotate about axis x. In someembodiments, axis x is perpendicular to axis y. The gears 112 and 94 areselected to provide the desired gear ratio, which may vary depending onthe application.

Referring now to FIG. 10, a perspective view of a two-stroke engine 22′is provided that illustrates an accessory connected to receive oil fromthe closed-loop oiling system. Components of two-stroke engine 22′remain relatively the same as that described with respect to FIGS. 3-6.However, in this embodiment, two-stroke engine 22′ further includes anaccessory 122. In the embodiment shown in FIG. 10, accessory 122 is ahigh-pressure direct injection (HPDI) pressure pump assembly that iscoupled to crankshaft 60 via belt 124. Although shown as being driven bya belt 124, in some embodiments, the accessory 122 can be driven by achain, gear set, or in any other suitable way. In this embodiment, oneor more cam lobes (not visible) included as part of the HPDI pressurepump assembly 122 are utilized to convert rotational motion to linearmotion/actuation of accessories associated with engine 22′. Lubricationof the cam lobes is provided by oil pump 44′, which provides pressurizedoil via line 120 to HPDI pressure pump assembly 122. Line 120 may be aflexible hose or a hard tube, depending on the application. In otherembodiments, accessory 122 may be utilized in applications other thanHPDI pressure pump assembly.

Oil provided to accessory 122 is returned to oil tank 42 (shown in FIG.5). In some embodiments, because accessory 122 is located above oil pump44′ and oil tank 42, pressurized oil provided to accessory 122 isreturned to oil tank 42 by way of gravity. In other embodiments,however, a sump and scavenge pump may be relied upon to return oil tooil tank 42 as part of the closed-loop pressurized oiling system. Inaddition, in some embodiments a pressure regulator may be connectedbetween oil pump 44′ and accessory 122—e.g., along line 120—to regulatethe pressure of oil provided to accessory 122. In some embodiments, line120 is flexible while in some embodiments it is formed from a stiffmaterial. In some embodiments, the pressure regulator may be connectedto oil tank 42 (as shown in FIG. 5), in which excess oil is directed tooil tank 42 to maintain a desired oil pressure, for example via abypass. In some embodiments, the pressure regulator is incorporated aspart of oil pump 44′.

In some embodiments, accessory 122 requires oil pressure greater thanthat provided by the total loss oiling system (i.e., first oiling system30) connected to provide oil to engine 22. In particular, in someembodiments, oil pressure greater than 10 PSI is provided to accessory122. In some embodiments, an oil pressure greater than 20 PSI isprovided to accessory 122, and in some embodiments an oil pressuregreater than 40 PSI is provided to accessory 122.

Referring now to FIGS. 11A-11B, an embodiment of a snowmobile 10′ isillustrated that employs a turbocharger 130 configured to providecompressed air to the cylinders, wherein a second oiling system (i.e.,closed-looped oiling system) is utilized to provide pressurized oil tothe turbocharger 130. In particular, FIGS. 11A and 11B are side views ofsnowmobile 10′ that illustrates a possible position of turbocharger 130relative to engine 22″. In the embodiment shown in FIGS. 11A and 11B,snowmobile 10′ includes track 12′, seat 14′, one or more skis 16′, hood18′, handlebars 20′ and engine 22″ (partially obscured by hood 18). Asdiscussed in more detail below, engine 22″ includes a first oilingsystem and a second oiling system. The first oiling system is a totalloss oiling system utilized to lubricate engine 22″. The second oilingsystem is a pressurized, closed-loop oiling system utilized to providelubrication to one or more accessories associated with engine 22″,including at least turbocharger 130. The second oiling system includesat least one pump (not visible in this view), mechanically coupled tothe engine 22″ to provide the desired oil pressure—for example greaterthan that provided in the first oiling system. Utilizing a second oilingsystem, distinct from the first oiling system, allows engine 22″ to makeuse of accessories—such as turbocharger 130—that requires a higher oilpressures than that made available in a typical two-stroke enginerelying on a total loss oiling system.

As discussed in more detail below, turbocharger 130 is connected toreceive exhaust from engine 22″, wherein mechanical energy is extractedfrom the flow of the exhaust and utilized to drive a compressor thatprovides compressed air for mixture with the fuel provided to thecylinders. In the embodiment shown in FIGS. 11A-11B, the compressed airis cooled by intercooler 142 prior to mixing with fuel. In oneembodiment, intercooler 142 may be an air-to-air intercooler or awater-to-air intercooler.

In the embodiment shown in FIGS. 11A and 11B, turbocharger 130 ispositioned adjacent to engine 22″, with intercooler 142 positioned infront of engine 22″. In other embodiments, the location of intercooler142 relative to engine 22″ may be modified. For example, in someembodiments, intercooler 142 may be positioned behind engine 22″ orabove engine 22″. Air compressed by turbocharger 130 is provided tointercooler 142, to cool the compressed air prior to provision to airintake ports (not shown in this view). The second oiling system isconnected to provide lubrication to turbocharger 130. As a closed-loopoiling system, oil provided to turbocharger 130 is returned to the oiltank (e.g., oil tank 42 shown in FIG. 11C or oil tank 42″ shown in FIG.12).

FIG. 12 is a perspective view illustrating the relative positions ofturbocharger 130, intercooler 142, oil tank 42″ and an oil pump(obscured by oil tank 42″) according to some embodiments. Turbocharger130 is connected to receive oil from the closed-loop oiling system(i.e., second oiling system 32 shown in FIG. 2), which includes an oilpump (e.g., similar to oil pump 44 shown in FIG. 3 and/or oil pump 44′shown in FIG. 10) and oil tank 42″ (wherein the oil pump is obscured byoil tank 42″). In some embodiments, the turbocharger 130 is utilized inconjunction with another accessory such as the one described withrespect to FIG. 10. In some embodiments, the turbocharger 130 is usedwithout the additional accessory described with respect to FIG. 10. Insome embodiments, however, the turbocharger 130 can be used inconjunction with one or more additional accessories, such as the HPDIsystem previously described. In some embodiments, turbocharger 130includes exhaust inlet port 134, exhaust outlet port 136, air inlet port138, and compressed air outlet port 140. In general, a turbochargeroperates by receiving exhaust provided by engine 22″ (see exhaust path132). The exhaust is provided to exhaust inlet port 134. A turbinelocated within the turbocharger 130 is utilized to extract energy (e.g.,mechanical power) from the received exhaust. The mechanical energyextracted by the turbine (not shown) is utilized to provide power to acompressor (not shown), which compresses air received at air inlet port138 to provide compressed air at compressed air outlet port 140. Thecompressed air is provided to the air intake ports (of which, air intakeport 58 a is visible) of two-stroke engine 22″.

In some embodiments, such as that shown in FIG. 12, compressed air isprovided to an intercooler 142 to cool the compressed air prior to beingprovided to air intake port. In the embodiment shown in FIG. 12,intercooler is connected to receive compressed air from turbocharger 130via air intake port 144. Intercooler cools the received compressed air,and outputs the cooled, compressed air to air intake ports via outputport 146. Air output port 146 may be integrally formed with intercooler142, or may be attached to intercooler 142. In some embodiments, such asthat shown in FIG. 12, intercooler 142 is an air-to water intercoolerutilizing a liquid coolant to remove heat from the compressed air. Insome embodiments, the turbocharger is utilized without an intercooler142.

Oil provided to turbocharger 130 is returned to oil tank 42″. In someembodiments, because turbocharger 130 is located above and oil tank 42″,pressurized oil provided to turbocharger 130 is returned to oil tank 42″by way of gravity. In particular, in some embodiments, the oil outletport of turbocharger 130 (shown in FIG. 13B as oil outlet port 150) ispositioned above (i.e., at a higher elevation) oil tank 42″, and inaddition oil tank 42″ is positioned above the inlet to the oil pump,such that gravity is utilized to move oil from the oil outlet ofturbocharger 130, to oil tank 42″, and to the inlet of the oil pump.However, in some embodiments, due to the inclination of the snowmobileon various terrain or other anomalies that may prevent oil from drainingback into oil tank 42″, a scavenge pump (and in some embodiments a sump)may be relied upon to return oil to oil tank 42″ as part of theclosed-loop pressurized oiling system (as shown in FIG. 15). Inaddition, in some embodiments, a pressure regulator may be connectedbetween the oil pump and turbocharger 130 to regulate the pressure ofoil provided to turbocharger 130. The regulator may return excess oil tooil tank 42″ (or any other desirable part of the system) in order tomaintain a desired oil pressure. In other embodiments, the pressureregulator is incorporated as part of the oil pump.

In some embodiments, turbocharger 130 requires an oil pressure greaterthan that provided to the engine as part of the total loss oilingsystem. In some embodiments, oil pressure provided to the turbocharger130 is greater than 10 PSI. In some embodiments, oil pressure providedto turbocharger 130 is greater than 20 PSI. In some embodiments, oilpressure provided to turbocharger 130 is greater than 40 PSI.

Referring now to FIGS. 13A and 13B, perspective views of a turbocharger130 are shown according to some embodiments. Turbocharger 130 once againincludes exhaust inlet port 134, exhaust outlet port 136, air inlet port138, and compressed air outlet port 140. FIG. 13A illustrates thelocation of oil inlet port 148 connected to receive pressurized oil fromthe oil pump (e.g., oil pump 44 as shown in FIG. 3 or oil pump 44′ shownin FIG. 10). In this embodiment, oil inlet port 148 is located on a topside of turbocharger 130. Oil provided at oil inlet port 148 may beprovided at a pressure regulated by the oil pump and/or pressureregulator located internal to the oil pump or connected between the oilpump and oil inlet port 148. Oil provided at oil inlet port 148 isutilized to lubricate components of turbocharger 130, such as bearings.After being used to lubricate turbocharger, the oil exits turbocharger130 via oil outlet port 150 and is returned to oil tank 42″ (as shown inFIG. 12). FIG. 13B illustrates the location of oil outlet port 150connected to return oil to oil tank 42″. In some embodiments, oil outletport 150 is located on the bottom of turbocharger 130. In someembodiments, oil tank 42″ is located below oil outlet port 150, suchthat oil exiting turbocharger 130 via oil outlet port 150 is returned tooil tank 42″ as a result of gravity. In some embodiments, a scavengepump (and in some embodiments a sump) is utilized to aid the return ofoil to oil tank 42″ as part of the closed loop pressurized oilingsystem.

Referring now to FIGS. 14A-14D, a coolant system is illustratedaccording to some embodiments. FIGS. 14A-14C are perspective viewsillustrating the connections of the coolant system and location relativeto engine 22″, and FIG. 14D is a top view that illustrates the flow ofcoolant through the coolant system according to some embodiments. In theembodiment shown in FIGS. 14A-14C, turbocharger 130 has been removedfrom the view to better illustrate coolant system. An embodimentillustrating the connection of the turbocharger 130 to the coolantsystem is illustrated in FIG. 14D.

In the embodiment shown in FIGS. 14A-14C, the coolant system includescoolant tank 152, which in some embodiments includes a cap, hose/tube154, 158, and 160, heat exchanger 162. In at least some embodiments, theheat exchanger 162 includes cooling channel(s) 164 a, 164 b. In someembodiments, coolant is utilized to extract heat from the compressed airprovided to intercooler 142. Coolant is stored in coolant tank 152, inconjunction with the rest of the system, and provided to intercooler 142via hose/tube 154. Intercooler 142 includes a coolant inlet port 156 afor receiving coolant, which is then directed through intercooler 142 toextract heat from the compressed air provided by turbocharger 130 (notshown in this view). Coolant exits intercooler 142 via coolant outputport 156 b, and is provided to a water pump (not shown in this view, butshown in FIG. 14D as water pump 166). The water pump pumps the coolantreceived from intercooler 142 through engine 22″, and then throughvarious components to remove/extract heat from the coolant before theprocess is repeated. In addition, coolant may in some embodiments beprovided to other accessories such as turbocharger 130 and/or otheraccessories to provide heat removal. In some embodiments, coolant outputport 156 b of intercooler 142 is elevated relative to water pump 166 toallow coolant pumped through intercooler 142 to be provided via gravityto water pump 166. In some embodiments, coolants is provided by heatexchangers 162 (e.g., through or cooling channels 164 a, 164 b)—at whichpoint the coolant is at a lowest temperature within the coolingcircuit—is provided first to intercooler 142, and then to engine 22″. Abenefit of this approach is that, in some embodiments, it maximizes thecooling effect of intercooler 142 (e.g., maximum cooling of thecompressed air provided by turbocharger 130 to intercooler 142). Inother embodiments, coolant may be pumped separately to intercooler 142and engine 22″, in parallel fashion rather than being provided first toone component and then to another.

Referring to FIG. 14D, a coolant flow path according to one or moreembodiments is illustrated. As illustrated in FIG. 14D, the coolant flowpath is a closed-loop system in which coolant is circulated to transferthermal energy as required. Coolant is added to the system via the capassociated with coolant tank 152. In some embodiments, the coolant flowpath comprises one or more coolant loops. In some embodiments, waterpump 166 provides coolant to the one or more coolant loops. However, inother embodiments, additional water pumps may be utilized to separatelyprovide coolant to each coolant loop. In some embodiments the firstcoolant loop includes the intercooler 142 and engine 22″, and a secondcoolant loop that includes throttle bodies 170 and turbocharger 130. Thefirst coolant loop provides coolant from heat exchanger 162 viahose/tube 154 to intercooler 142. The relative temperature of coolantprovided from heat exchanger 162 to intercooler 142 is lower thanelsewhere in the cooling circuit. The coolant (relatively lowtemperature) flows through intercooler 142 from coolant inlet port 156 ato coolant output port 156 b. The coolant flows from intercooler 142 towater pump 166 via hose/tube 158. The coolant provided from intercooler142 extracts thermal energy from the intercooler to cool the compressedair provided to the engine 22″. Thus, the temperature of the coolantleaving intercooler 142 via hose/tube 158 may be higher than thetemperature of the coolant provided to intercooler 142. Subsequently,the coolant is provided to water pump 166 (which may also contain acavity, reservoir, etc. for coolant), which pumps the coolant throughthe cooling circuit(s). In some embodiments, the coolant is directed tothe engine 22″ and then the coolant returns to the heat exchanger 162via hose/tube 160. In general, coolant exiting the engine 22″ viahose/tube 160 is at a temperature higher than that provided tointercooler 142.

In some embodiments, another or second coolant loop includes throttlebody 170 and engine accessory—such as turbocharger 130. Water pump 166pumps coolant to throttle body 170 via tube/hose 168, and then via tubehose 172 to turbocharger 130. However, in some embodiments the coolantmay be pumped through turbocharger 130 and then through throttle body170. In some embodiments, coolant is used to heat the throttle body (orthrottle bodies) 170 in order to prevent freezing/icing in snow vehicleapplications. Coolant provided to turbocharger 130 is returned to waterpump/reservoir 166 via tube hose 174. In some embodiments, the two ormore coolant flow paths are not separate paths, but instead result inthe coolant from the two or more coolants paths mixing in the engine22″, water pump 166, and heat exchanger(s) 162.

To dissipate heat from the coolant, the coolant is provided to heatexchanger 162 and cooling channels 164 a and 164 b. These components aredesigned to extract heat from the coolant flowing through them, suchthat the coolant can be returned at a sufficiently low temperature toprovide cooling. In the embodiment shown in FIG. 14D, coolant (nowrelatively cool) exits the heat exchanger 162 and is provided viahose/tube 154 to intercooler 142.

The embodiment of the cooling circuit shown in FIG. 14D provides coolantto intercooler 142, and coolant exiting intercooler 142 is provided towater pump 166. In this way, coolant provided to intercooler 142 islikely to be a temperature that is low relative to the temperature ofthe coolant in other parts of the cooling circuit. This assures that thetemperature of the coolant provided to the intercooler is low relativeto other parts of the cooling circuit, to provide maximum cooling of thecompressed air provided by the turbocharger 130 to the intercooler 142.In other embodiments, the order in which coolant is pumped tointercooler 142, turbocharger 130, throttle body 170, and/or engine 22″may be varied. In still other embodiments, the air-to-water intercoolershown in FIG. 14D is implemented as an air-to-air intercooler, in whichintercooler 142 would not be included as part of the coolant circuit.

In some embodiments, the intercooler 142 is located forwardly of theengine 22″; in some embodiments, however, the intercooler 142 can belocated above, below, behind, or to a side of the engine 22″. In someembodiments, multiple intercoolers are utilized, for example one on eachside of the engine 22″.

Referring now to FIG. 15, a perspective view of a two-stroke engine 22′″is shown that illustrates a stacked configuration of first and secondoil pumps 44 a and 44 b. First oil pump 44 a includes inlet/outlet ports68 a and 68 b, and second oil pump 44 b includes inlet/outlet ports 68 cand 68 d. In the embodiment shown in FIG. 15, the size of oil pumps 44 aand 44 b are approximately the same, as are the size of inlet/outletports 68 a-68 d. However, in other embodiments the first and second oilpumps 44 a and 44 b may be sized differently, according to therespective roles of each. Similarly, the size of inlet/outlet ports 68a-68 d may be sized differently based on the application.

As illustrated in FIG. 15, oil pumps 44 a and 44 b are located adjacentto one another, in a stacked configuration along the axis of the shaftdriving oil pumps 44 a and 44 b (e.g., perpendicular to the axis definedthrough the crankshaft 60). Both pumps 44 a and 44 b are thereforedriven by the same shaft mechanically coupled to crankshaft 60 (notvisible in this view). In some embodiments, first oil pump 44 a is apressurized oil pump that provides pressurized oil to one or moreaccessories, and second oil pump 44 b is a scavenge pump that aids inreturning oil from the one or more accessories to oil tank 42 (not shownin this view). In some embodiments, first oil pump 44 a is a scavengeoil pump that aids in returning oil from the one or more accessories tooil tank 42 (not shown in this view), and second oil pump 44 b is apressurized oil pump that provides pressurized oil to one or moreaccessories.

Referring now to FIGS. 16A-16F, block diagrams of a pressurized oilingsystem (or closed loop-oiling system, such as that described in FIG. 2)according to various embodiments. It should be noted that a vehiclewill, in at least some embodiments, also include a first oilingdistribution system, such as a total-loss oiling system, that isutilized to lubricate the engine. The pressurized oiling system isseparate from the first or total loss oiling system.

In particular, FIG. 16A illustrates a pressurized oiling system 180 thatincludes oil filter 182, accessory 184, scavenge pump reservoir 186,scavenge pump 188, oil reservoir 190, pressure pump 192, oil pressureregulator 194, and two-stroke engine 196. As shown in FIG. 16A, in someembodiments, pressure pump 192 and scavenge pump 188 are mechanicallycoupled to two-stroke engine 196, for example via a common shaft drivingboth pumps. Mechanical power developed by two-stroke engine 196 isprovided to pressure pump 192 and scavenge pump 188. For example,pressure pump 192 and scavenge pump 188 may be located adjacent oneanother in a stacked configuration, such as that shown in FIG. 15.Pressure pump 192 is fluidly connected to pump oil from oil reservoir190 to oil pressure regulator 194. Oil pressure regulator 194 maintainsthe oil provided by pressure pump 192 at a desired pressure. In theembodiment shown in FIG. 16A, if the pressure exceeds a desiredpressure, excess oil is directed back to oil reservoir 190 via excessoil path 198. Oil filter 182 filters pressurized oil provided by oilpressure regulator 194 and provides filtered oil to accessory 184. Forexample, as discussed above, accessories requiring pressurized oil mayinclude turbochargers, HPDI pressure pump assembly, etc. As providedabove, accessories may include any devices requiring pressurized oil forlubrication. Pressurized oil provided to accessory 184 for lubricationis returned to scavenge pump reservoir 186. Scavenge pump 188 pumps oilcollected in scavenge pump reservoir 186 to oil reservoir 190. In someembodiments, the pressurized oiling system(s) described herein can alsoinclude an oil cooler in any suitable location in the circuit.

FIG. 16B illustrates a pressurized oiling system 200 that includes thesame components described with respect to FIG. 16A. In the embodimentillustrated in FIG. 16B, the position of oil filter 182 and oil pressureregulator 194 in the oil flow diagram are switched. As a result,pressurized oil pumped by pressure pump 192 is provided to oil filter182 and then to oil pressure regulator 194. In the event pressurized oilprovided to oil pressure regulator 194 exceeds the desired pressure,overflow oil is directed back to oil reservoir 190 via excess oil path198.

FIG. 16C illustrates a pressurized oiling system 202 that includes thesame components described with respect to FIG. 16A. However, in theembodiment shown in FIG. 16C, instead of a single accessory, two or moreaccessories 184 a and 184 b are connected in parallel to receivepressurized oil. In particular, pressurized oil pumped from pressurepump 192 is provided to oil pressure regulator 194 and oil filter 182,wherein the first accessory 184 a and the second accessory 184 b areconnected in a parallel configuration to receive pressurized oil fromthe oil pressure regulator 194 and oil filter 182. In one embodiment,pressurized oil provided to first and second accessories 184 a and 184 bis provided at a single pressure to both accessories. In someembodiments, however, oil can be provided at different pressures tofirst and second accessories 184 a and 184 b, for example via anadditional pressure regulator or, in some embodiments, where the firstand second accessories are in series. Oil collected from first andsecond accessories 184 a and 184 b are collected in scavenge pumpreservoir 186, and pumped by scavenge pump 188 to oil reservoir 190.

FIG. 16D illustrates a pressurized oiling system 204 that includes thesame components described with respect to FIG. 16C. However, in theembodiment shown in FIG. 16D, first and second accessories 184 a and 184b are connected in a serial configuration, rather than in the parallelconfiguration as shown in FIG. 16C. That is, pressurized oil from oilfilter 182 is provided to first accessory 184 a, and oil discharged fromfirst accessory 184 a is provided to second accessory 184 b. Oildischarged from second accessory 184 b is returned to scavenge pumpreservoir 186, where it is pumped by scavenge pump 188 to oil reservoir190. As a result of first and second accessories 184 a and 184 b beingconnected in series to receive pressurized oil, the oil pressureprovided to accessory 184 a may differ from the oil pressure provided toaccessory 184 b. In some embodiments, the accessory requiring higherpressure oil may be connected first in series to receive pressurized oilfrom oil filter 182.

FIG. 16E illustrates a closed-loop oiling system 206 that includes thesame components described with respect to FIG. 16A. However, in theembodiment shown in FIG. 16E, the position of scavenge pump 188 andpressure pump 192—relative to two-stroke engine 196—are exchanged. Inparticular, assuming scavenge pump 188 and pressure pump 192 areconnected in a stacked configuration, scavenge pump 188 is locatedbetween two-stroke engine 196 and pressure pump 192. Depending on thephysical size of scavenge pump 188 and pressure pump 192, it may beadvantageous to locate either scavenge pump 188 or pressure pump 192closer to two-stroke engine 196.

FIG. 16F illustrates a pressurized oiling system 208 that includes oilfilter 182, accessory 184, scavenge pump reservoir 186, scavenge pump188, oil reservoir 190, pressure pump 210 including an internalregulator, and two-stroke engine 196. In the embodiment shown in FIG.16F, pressure pump 210 and scavenge pump 188 are mechanically coupled totwo-stroke engine 196, for example via a common shaft driving bothpumps. Mechanical power developed by two-stroke engine 196 is providedto pressure pump 210 and scavenge pump 188. For example, pressure pump210 and scavenge pump 188 may be located adjacent one another in astacked configuration, such as that shown in FIG. 15. Pressure pump 210is fluidly connected to pump oil from oil reservoir 190 to accessory184. In contrast with the embodiment shown in FIG. 16A, pressure pump210 includes an internal oil pressure regulator that maintains the oilprovided by the pump at a desired pressure. In the embodiment shown inFIG. 16F, if the pressure exceeds a desired pressure, excess oil isdirected back to oil reservoir 190 via excess oil path 212. Oil filter182 filters pressurized oil provided by oil pressure regulator 194, andprovides filtered oil to accessory 184. For example, as discussed above,accessories requiring pressurized oil may include turbochargers, HPDIpressure pump assembly, etc. As provided above, accessories may includeany devices requiring pressurized oil for lubrication. Pressurized oilprovided to accessory 184 for lubrication is returned to scavenge pumpreservoir 186. Scavenge pump 188 pumps oil collected in scavenge pumpreservoir 186 to oil reservoir 190.

The oil distribution system described herein allows for the availabilityof pressurized oil to one or more accessories in a two-stroke engineenvironment. To provide pressurized oil, the system comprises a firstoiling system and a second oiling system distinct from the first oilingsystem. The first oiling system may be a typical total-loss system thatdistributes oil from a first oil tank to the two-stroke engine at afirst oil pressure. The second oiling system includes a pumpmechanically coupled to the crankshaft of the two-stroke engine todistribute oil from a second oil tank to an accessory at a second oilpressure, wherein the second oil pressure is greater than the first oilpressure. In this way, the second oiling system powered by thetwo-stroke engine provides pressurized oil.

Although shown in relation to a snowmobile, the oiling systems, coolingsystems, etc. described herein can also be used with ATVs, outboardengines, unmanned aerial vehicles, airplanes, personal watercraft,side-by-side off-road vehicles, etc.

Referring now to FIGS. 17A-17D, block diagrams of engine systemsutilizing a parallel-path exhaust are provided according to someembodiments. In general, the embodiment shown in FIG. 17A illustrates anengine system 220 that utilizes an external wastegate 228, theembodiment shown in FIG. 17B illustrates an engine system 220′ thatutilizes a turbocharger internal wastegate 242′, the embodiment shown inFIG. 17C illustrates an engine system 220″ that includes a turbochargerinternal wastegate 242″ and a fixed flow orifice 244 from the turnedexpansion chamber to the exhaust muffler, and FIG. 17D illustrates anengine system 220′″ that includes both a turbocharger internal wastegate242′″ and an external wastegate 228″.

In some embodiments, such as that shown in FIG. 17A, engine system 220includes exhaust manifold 224, tuned expansion chamber 226, externalwastegate 228, exhaust muffler 230, turbocharger 232, which includesexhaust turbine 234 and compressor 236, charge air cooler 238 and intakeplenum 240. Compressed air provided by turbocharger compressor 236 iscooled by charge air cooler 238. In some embodiments, as described withrespect to FIGS. 14A-14D previously, charge air cooler 238 is connectedto a coolant circuit that includes both the charge air cooler 238 andtwo-stroke engine 222. In some embodiments, charge air cooler 238 isconnected to receive coolant from the heat exchanger, and coolantexiting charge air cooler 238 is provided to two-stroke engine 222. Thatis, in some embodiments, the charge air cooler 238 and two-stroke engine222 are connected in series to form the coolant circuit, and coolant isprovided first to the charge air cooler 238. In other embodiments, otherconfigurations of coolant circuits may be utilized to cool the chargeair cooler 238 and two-stroke engine 222.

Exhaust generated by two-stroke engine 222 is provided to exhaustmanifold 224. For example, in embodiments in which two-stroke engine 222includes first and second cylinders, exhaust manifold would includefirst and second inlets connected to receive exhaust from the first andsecond cylinders, respectively. In other embodiments, exhaust manifoldmay include fewer or additional inlets for receiving exhaust generatedby the two-stroke engine 222. Exhaust manifold 224 bifurcates theexhaust received from two-stroke engine 222 into first and secondparallel paths. In some embodiments the first parallel path includestuned expansion chamber 226 and external wastegate 228, and the secondparallel path includes turbocharger 232 (specifically exhaust turbine234). Exhaust provided to the first parallel path and the secondparallel path is provided to exhaust muffler 230, which discharges theexhaust to atmosphere. The mass/volume of exhaust provided to the firstand second parallel paths may be equal or unequal. In some embodiments,a wastegate is utilized to control the flow of exhaust provided to theturbocharger 232. In some embodiments the wastegate is external—as shownin FIG. 17A which includes external wastegate 228—and located on theparallel path that includes tuned expansion chamber 226. In someembodiments, the wastegate is internal to the turbocharger and istherefore located on the parallel path that includes the turbocharger(as shown in FIG. 17B, which includes internal wastegate 242′).

Tuned expansion chamber 226—sometimes referred to as a tuned pipe—isutilized to improve the efficiency of two-stroke engines. Specifically,high-pressure gas exiting a combustion cylinder flows in the form of awavefront as exhaust gas is pushed into the expansion chamber. Thechange in cross-section of the expansion chamber results in a portion ofthe wavefront being reflected back toward the exhaust manifold 224 andthe respective combustion cylinder. The cross-section and length of thetuned expansion chamber 226 is designed to generate reflections thatarrive at the inlet of exhaust manifold 224 to push any escaped fuel/airmixture back into the combustion cylinder prior to the next combustioncycle, thereby improving the efficiency of the two-stroke engine. Insome embodiments, the temperature of exhaust within the tuned expansionchamber 226 effects the reflections generated by tuned expansion chamber226. As described in more detail below, external wastage 228 can beutilized to control the temperature within the tuned expansion chamber226, and can therefore be utilized to control the performance of thetuned expansion chamber 226.

In some embodiments, external wastegate 228 regulates the exhaust gaswithin the tuned expansion chamber 226 and therefore also regulates themass and/or volume of exhaust flowing through the turbocharger 232. Forexample, in some embodiments external wastegate 228 is actuated (e.g.,opened or closed) in response to exhaust pressure exerted on theexternal wastegate. In some embodiments, an increase in exhaust pressurecauses a valve on the external wastegate 228 to open, while a decreasein exhaust pressure causes the valve on the external wastegate 228 toclose. In some embodiments, the valve associated with external wastegate228 is actuated in response to the outlet pressure of the turbochargercompressor 236, referred to as the “turbo boost pressure”. In otherembodiments, actuation of external wastegate 228 may be controlled by anengine control unit (ECU) (not shown) based on one or more measuredinputs, including one or more of exhaust pressure, exhaust temperature,exhaust flow through the turbocharger, turbo boost pressure, etc. Forexample, in some embodiments external wastegate 228 is controlled (i.e.,actuated) based on exhaust temperature within the tuned expansionchamber 226, wherein temperature is increased by opening (partially orcompletely) the external wastegate 228 and decreased by closing(partially or completely) the external wastegate 228. In someembodiments, external wastegate 228 is controlled based on the desiredflow of exhaust through turbocharger 232, wherein external wastegate 228is closed (partially or completely) to increase the flow of exhaustthrough turbocharger 232 and opened (partially or completely) todecrease the flow of exhaust through turbocharger 232. In someembodiments, a combination of inputs (e.g., temperature within tunedexpansion chamber, flow of exhaust through the turbocharger, etc.) areutilized to determine the actuation of external wastegate 228.

Exhaust exiting external wastegate 228 is provided to exhaust muffler230. In some embodiments, exhaust provided by external wastegate 228(i.e., the first parallel path) is re-combined with exhaust from theturbocharger 232 (i.e., the second parallel path) prior to provision toexhaust muffler 230. In other embodiments, exhaust muffler 230 isconnected individually to both the external wastegate 228 andturbocharger 232 (i.e., first and second parallel paths).

As shown in FIGS. 17A and 17B, turbocharger 232 includes exhaust turbine234 and compressor 236. During operation, exhaust gas provided byexhaust manifold 224 to the second parallel path is provided to exhaustturbine 234, which extracts energy from the exhaust gas and utilizes theextracted energy to drive compressor 236. Exhaust utilized by exhaustturbine 234 exits and is provided to exhaust muffler 230. In someembodiments, the pipe utilized to communicate exhaust from exhaustturbine 234 to exhaust muffler 230 is configured to receive exhaust fromexternal wastegate 228, such that only a single exhaust carrying pipe isprovided to exhaust muffler 230. In other embodiments, the exhaust pipeutilized to communicate exhaust from exhaust turbine 234 to exhaustmuffler 230 is connected directly to exhaust muffler 230. In someembodiments, locating turbocharger 232 in close proximity to exhaustmanifold 224 increases the responsiveness of the turbocharger.

Compressor 236 compresses atmospheric air and provides the compressedair to charge air cooler 238, which acts to cool the air prior to thecompressed air being provided to the engine for combustion. Compressed,cooled air is provided to intake plenum 240, which provides the cooled,compressed air to the respective combustion chambers for combustion.Reducing the temperature of the compressed air increases the energydensity of the air supplied to two-stroke engine 222. A benefit ofutilizing a first and second parallel exhaust path is that the benefitsof a tuned expansion chamber are retained while also allowingturbocharger to be located in relatively close proximity to thetwo-stroke engine 222, which increases the responsiveness of theturbocharger to operating changes of the two-stroke engine.

In another embodiment, illustrated in FIG. 17B, rather than utilize anexternal wastegate connected to the outlet of the tuned expansionchamber 226 to control the flow of exhaust through the turbocharger 232,an internal wastegate 242′ is provided in parallel with turbochargerexhaust turbine 234′. In some embodiments, turbocharger exhaust turbinehousing 233′ bifurcates the flow of exhaust into two parts, one providedto turbocharger internal wastegate 242′ and one provided to turbochargerexhaust turbine housing 234′. Internal wastegate 242′ controls the flowof exhaust through the exhaust turbine 234′ by providing an alternatepath for exhaust to bypass the exhaust turbine 234′. In someembodiments, the presence of internal wastegate 242′ negates thenecessity for an external wastegate, and the tuned expansion chamber226′ is closed (i.e., does not include an outlet to exhaust muffler230′, as shown in FIG. 17B).

As described with respect to external wastegate 228 shown in FIG. 17A,in some embodiments internal wastegate 242′ is actuated (e.g., opened orclosed) in response to exhaust pressure exerted on the internalwastegate 242′. In some embodiments, an increase in exhaust pressurecauses a valve on the internal wastegate 242′ to open, while a decreasein exhaust pressure causes the valve on the internal wastegate 242′ toclose. In other embodiments, the valve associated with internalwastegate 242′ is actuated in response to the outlet pressure of theturbocharger compressor 236′ (i.e., turbo boost pressure). In someembodiments, actuation of internal wastegate 242′ may be controlled byan engine control unit (ECU) (not shown) based on one or more measuredinputs, including one or more of exhaust pressure, exhaust temperature,exhaust flow through the turbocharger, turbo boost pressure, etc. Forexample, in some embodiments internal wastegate 242′ is controlled(i.e., actuated) based on exhaust temperature within the tuned expansionchamber 226, wherein temperature is decreased by opening (partially orcompletely) the internal wastegate 242′ and increased by closing(partially or completely) the internal wastegate 242′. In someembodiments, internal wastegate 242′ is controlled based on the desiredflow of exhaust through turbocharger exhaust turbine 234′, whereininternal wastegate 242′ is closed (partially or completely) to increasethe flow of exhaust through turbocharger exhaust turbine 234′ and opened(partially or completely) to decrease the flow of exhaust throughturbocharger exhaust turbine 234′. In some embodiments, a combination ofinputs (e.g., temperature within tuned expansion chamber, flow ofexhaust through the turbocharger, etc.) are utilized to determine theactuation of internal wastegate 242′.

In other embodiments (shown in FIGS. 17C and 17D) both an internalwastegate and some sort of output from the tuned expansion chamber tothe exhaust muffler is utilized in conjunction with one another. Forexample, in some embodiments such as that shown in FIG. 17C, a fixedflow orifice 244″ provides exhaust from tuned expansion chamber 226″ toexhaust muffler 230″. In this embodiment, the flow of exhaust providedby fixed flow orifice 244″ to exhaust muffler 230″ is relatively fixeddue to the fixed size of the orifice. In some embodiments, utilizing afixed flow orifice 244″ allows exhaust to flow through tuned expansionchamber to regulate (e.g., raise) exhaust temperatures in the tunedexpansion chamber 226″. In this embodiment, turbocharger internalwastegate 242″ is utilized to selectively control the flow of exhaustthrough turbocharger exhaust turbine 234″. Control of the turbochargerinternal wastegate 242″ may utilize one or more of the inputs describedwith respect to FIGS. 17A and/or 17B. For example, in some embodimentsactuation of turbocharger internal wastegate 242″ is based on the turboboost pressure.

In some embodiments, rather than a fixed flow orifice, an externalwastegate 228′″ is utilized in conjunction with turbocharger internalwastegate 242′″ to selectively regulate the flow of exhaust from tunedexpansion chamber 226′″ to exhaust muffler 230′″. In addition, in someembodiments, turbocharger internal wastegate 242′″ selectively regulatesthe flow of exhaust through turbocharger exhaust turbine 234″. In someembodiments, the external wastegate 228′″ is actuated based on one ormore inputs (e.g., temperature within the tuned expansion chamber,exhaust pressure within tuned expansion chamber, etc.) and the internalwastegate 242′″ is actuated based on one or more inputs, which may bethe same or different than those utilized to actuate external wastegate228′″ (e.g., exhaust pressure within the turbocharger, etc.). Onceagain, tuned expansion chamber 226′″ has a cross-section and/or lengthdesigned to generate a reflected wavefront time to arrive at the inletport of exhaust manifold 224′″ to push any escaped fuel/air mixture backinto the cylinder prior to the next combustion cycle. In someembodiments, external wastegate 228′″ is actuated based on temperaturemeasured within the tuned expansion chamber 226′″ and turbochargerinternal wastegate 242′″ is actuated based on the flow of exhaustprovided to the turbocharger exhaust turbine 234′″ and/or on the turboboost pressure. In some embodiments, one or both of the internalwastegate 242′″ and external wastegate 242′″ are regulated by an ECU andthe characteristics of each can be regulated based on pressure, flow,temperature, engine RPM, load, and the state (e.g.,open/closed/partially open) of the other of the internal and externalwastegate.

In some embodiments, the exhaust manifold (e.g. exhaust manifold 224)bifurcates the flow of exhaust. In some embodiments, exhaust manifoldmay not be utilized to bifurcate the exhaust. In some embodiments,exhaust manifold may have a single outlet for providing exhaust toexpansion chamber 226 and expansion chamber 226 includes an additionaloutlet for providing a parallel path of exhaust to a turbocharger.

Referring now to FIGS. 18A-20B, various views of an engine system 220utilizing a parallel-path exhaust path are shown. In particular, FIGS.18A-18D illustrate the engine system 220 utilizing a parallel-pathexhaust path. FIGS. 19A-19B illustrate the parallel-path exhaust pathwith the two-stroke engine 222 removed for clarity. FIGS. 20A-20Billustrate the parallel-path exhaust path with two-stroke engine,exhaust muffler, and charge air cooler removed for clarity.

In some embodiments, two-stroke engine 222 includes first and secondcylinders. Compressed air provided by the turbocharger 232 and cooled bycharge air cooler 238 is provided to the respective cylinders by intakeplenum 240. Exhaust generated by the first and second cylinders oftwo-stroke engine 222 is provided to exhaust manifold 224. Variousgeometries of exhaust manifold may be utilized, as described in moredetail below. In general, exhaust manifold 224 bifurcates the exhaustprovided by two-stroke engine 222 into first and second parallel paths.In some embodiments, the mass and/or volume of exhaust provided to thefirst and second parallel paths may be equal or unequal, and may changebased on the operating condition of the two-stroke engine. In someembodiments, a first parallel path includes tuned expansion chamber 226,and a second parallel path includes turbocharger 232. As discussedabove, turbocharger 232 includes an exhaust turbine 234 and a compressor236. Exhaust turbine 234 extracts energy from the exhaust and utilizesthe extracted energy to drive compressor 236.

As shown in more detail in FIGS. 19B, 20B and 24A-24D, exhaust manifold224 includes first and second inlets 250 a, 250 b connected to receiveexhaust from first and second combustion cylinders, respectively. Inaddition, exhaust manifold 224 includes first outlet 252 and secondoutlet 254, wherein first outlet 252 provides exhaust to the firstparallel path (e.g., to tuned expansion chamber 226) and second outlet254 provides exhaust to the second parallel path (e.g., to turbocharger234). In some embodiments, first and second inlets 250 a, 250 b arelocated on the same horizontal plane, offset horizontally from oneanother along the plane as shown in FIG. 24D. In some embodiments, firstoutlet 252 and second outlet 254 are located on the same vertical plane,offset from one another in a vertical direction as shown in FIG. 24D. Insome embodiments, first and second inlets 250 a, 250 b and first outlet252 are located on approximately the same plane. That is, exhaustflowing into first and second inlets 250 a and 250 b continues along thedefined plane to first outlet 252. In some embodiments, second outlet254 is oriented at an angle relative to the plane that includes firstand second inlets 250 a, 250 b and first outlet 252. For example, in theembodiment shown in FIG. 24C, this angle is represented by angle α. Insome embodiments, angle α is less than ninety degrees. In someembodiments, angle α is approximately forty-five degrees. In otherembodiments, such as those described with respect to FIGS. 25A-25D,26A-26D, and 27A-27D, exhaust manifold 224 may utilize various othergeometries to bifurcate the exhaust as required by the application.

In some embodiments, such as those shown in FIGS. 18A-20B, turbocharger232 is connected to second outlet 254 (e.g., second parallel path). Inother embodiments, such as those shown in FIGS. 21A-21C, theturbocharger is connected to the first outlet (e.g., the first parallelpath). The determination of whether turbocharger 232 is connected to thefirst outlet 252 or second outlet 254 may be based on space constraintsor may be based on the flow characteristics associated with the firstoutlet 252 and second outlet 254. In addition, exhaust manifold 224 mayutilize various geometries for bifurcating exhaust into first and secondparallel paths, respectively. For example, in some embodiments first andsecond inlets 250 a, 250 b and first outlet 252 form a Y-shape, in whichfirst and second inlets 250 a, 250 b are on the same plane as firstoutlet 252. In this embodiment, second outlet 254 is located at an anglerelative to the Y-shaped geometry defined by the first and second inlets250 a, 250 b and first outlet 252. In some embodiments, this angle isless than ninety degrees. In some embodiments, this angle isapproximately forty-five degrees. In other embodiments, described inmore detail below, both first outlet 252 and second outlet 254 arelocated at defined angles relative to the horizontal plane defined byfirst and second inlets 250 a, 250 b.

In some embodiments, tuned expansion chamber 226 includes expansionchamber inlet 274 and expansion chamber outlet 276. In some embodiments,expansion chamber inlet 274 is connected to first outlet 252 of exhaustmanifold 224 to receive exhaust from both the first and secondcylinders. The length and cross-sectional geometry of tuned expansionchamber 226 is selected to reflect wavefronts associated with thereceived exhaust back toward the first and second inlets 250 a, 250 bwith an arrival timed to push any air/gas mixture drawn out of theengine back into the cylinder prior to the port closing before the nextcombustion cycle. In the embodiment shown in FIGS. 18A-20B, tunedexpansion chamber 226 is coupled to first outlet 252. In someembodiments, expansion chamber outlet 276 is coupled to externalwastegate 228 via wastegate inlet 278, which in turn is coupled viawastegate outlet 280 to exhaust pipe inlet 282 associated with exhaustpipe 264. As described above, external wastegate 228 regulates theexhaust gas within the tuned expansion chamber 226 and thereforeregulates the flow of exhaust through the turbocharger 232. Morespecifically, external wastegate 228 regulates the mass and/or volume ofexhaust provided to turbocharger 232 (specifically exhaust turbine 234).In some embodiments, exhaust from external wastegate 228 is provideddirectly to a separate exhaust inlet on exhaust muffler 230. In someembodiments, exhaust from external wastegate 228 (i.e., first parallelpath) is combined with exhaust from the turbocharger 232 (i.e., secondparallel path) for provision to exhaust muffler 230 via a single exhaustinlet.

Exhaust turbine 234 associated with turbocharger 232 includes an exhaustinlet 256 and exhaust outlet 258. In some embodiments, exhaust inlet 256is coupled to second outlet 254 of exhaust manifold 224 to provideexhaust to exhaust turbine 234. In some embodiments, exhaust outlet 258is coupled via exhaust pipe 264 to exhaust muffler 230. In someembodiments, compressor 236 associated with turbocharger 232 is locatedadjacent to exhaust turbine 234. In some embodiments, compressor 236includes an air inlet 262 and a compressed air outlet 260. Compressordraws atmospheric air through air inlet 262, compresses the air, andprovides the compressed air to charge air cooler 238 via air outlet 260and hose/tube 266. As discussed above, the compressed air is cooled bycharge air cooler 238 to increase the density of the air, which providesthe cooled, condensed air to intake plenum 240 via coupling 268. Airintake plenum 240 is connected to air intake manifold 270, whichprovides compressed air to first and second combustion cylinders viafirst and second air intakes 272 a and 272 b.

As shown in FIG. 18A, the length of the flow path of exhaust from thefirst and second cylinders of engine 222 to turbocharger 232 issignificantly less than the length of tuned expansion chamber 226. Abenefit of locating turbocharger 232 proximal to engine 222 (inparticular, in proximity to the exhaust ports associated with thecylinders) is improved responsiveness of turbocharger 232 to changes inrequested or commanded engine output. That is, the proximate location ofturbocharger relative to engine 222 decreases the time required forexhaust generated by engine 222 to be provided to turbocharger 232, andtherefore decreases the time required for the turbocharger to respond tochanges in requested or commanded engine output. As shown in the sideview illustrated in FIG. 18C, connecting turbocharger 232 to the secondparallel path (i.e., to the second outlet 254 associated with exhaustmanifold 224) results in turbocharger 232 being located on a horizontalplane that is above tuned expansion chamber 226. As discussed in moredetail below, in other embodiments turbocharger 232 may alternatively beconnected to the first parallel path and tuned expansion chamber 226 tothe second parallel path, which modifies the location of theturbocharger 232 relative to the tuned expansion chamber 226.

Referring now to FIGS. 21A-21B and 22A-22C, a parallel-path exhaustsystem 300 is illustrated in which turbocharger 302 is connected to thefirst outlet 342 of exhaust manifold 336 and tuned expansion chamber 304is connected to the second outlet 340 of exhaust manifold 336. In thisembodiment, first outlet 342 is located on the same vertical plane assecond outlet 340, wherein first outlet is located below second outlet340. This is in contrast with the embodiment illustrated with respect toFIGS. 17A-20B in which tuned expansion chamber was connected to thefirst outlet 252 and the turbocharger connected to the second outlet254. As a result of turbocharger 302 being connected to first outlet 342and tuned expansion chamber 304 being connected to second outlet 340,the relative locations of the turbocharger 302 and tuned expansionchamber 304 are modified as compared with previous embodiments. Inparticular, in some embodiments, turbocharger 302 may be located at avertical location lower than that shown in previous embodiments. In someembodiments, this may lower the center of gravity associated with theparallel-path exhaust system 300. In addition, the flow of exhaust fromthe exhaust manifold 336 into the turbocharger 302 and/or tunedexpansion chamber 304 may be varied as a result of the locations of eachas well as with respect to the geometry of the exhaust manifold 336.

In general, exhaust generated by two-stroke engine 222 is provided viafirst and second cylinders to exhaust manifold 336, which bifurcates theflow of exhaust into first and second parallel paths. In thisembodiment, the first parallel path includes turbocharger 302 and thesecond parallel path includes tuned expansion chamber 304 and externalwastegate 320. Turbocharger 302 extracts energy from the receivedexhaust and utilizes the extracted mechanical energy to drive acompressor that provides compressed air to intake plenum 240. Exhaustexits turbocharger 302 and is provided via exhaust pipe 326 to exhaustmuffler 324. Tuned expansion chamber 304 receives exhaust from exhaustmanifold 336, wherein external wastegate 320 regulates the exhaust gaswithin the tuned expansion chamber 304 and therefore regulates the flowof exhaust through the turbocharger 302. More specifically, externalwastegate 320 regulates the mass and/or volume of exhaust provided toturbocharger 302 (specifically exhaust turbine 308). Exhaust output fromexternal wastegate 320 is provided to exhaust muffler 324.

In the embodiment shown in FIGS. 22A-22C, exhaust manifold 336 includesfirst and second exhaust inlets 338 a, 338 b connected to receiveexhaust from first and second cylinders, respectively. In addition,exhaust manifold 336 includes first outlet 342 and second outlet 340,wherein first outlet 342 provides exhaust to the first parallel path andsecond outlet 340 provides exhaust to the second parallel path. In theembodiment shown in FIGS. 21A-21C, turbocharger 302 is connected tofirst outlet 342, and tuned expansion chamber 304 is connected to secondoutlet 340. In some embodiments, first and second exhaust inlets 338 a,338 b and first outlet 342 are located on the same plane, meaning thatexhaust flowing into first and second exhaust inlets 338 a, 338 b flowsinto first outlet 342 without requiring a change in direction. In thisembodiment, second outlet 340 is located at an angle β (shown in FIG.22C) relative to the Y-shaped geometry defined by the first and secondinlets 338 a, 338 b and first outlet 342. In some embodiments, thisangle β is less than ninety degrees. In some embodiments, the angle β isapproximately forty-five degrees. As a result, exhaust flowing intofirst and second exhaust inlets 338 a, 338 b is required to changedirection to enter tuned expansion chamber 304. In some embodiments, thelength and/or cross-sectional geometry of tuned expansion chamber 304takes into account the geometry of exhaust manifold 224 to ensure tunedexpansion chamber 304 provides the desired benefits to the efficiency ofthe two-stroke engine.

In some embodiments, tuned expansion chamber 304 includes expansionchamber inlet 316 and expansion chamber outlet 318, wherein outlet 318is coupled to external wastegate 320. In turn, external wastegateincludes wastegate inlet 322 and wastegate outlet 324. In someembodiment, wastegate outlet 324 is coupled either to the exhaust streamprovided by turbocharger 302 or directly to the exhaust muffler (notshown). In some embodiments, turbocharger 302 utilizes an internalwastegate to regulate the flow of exhaust provided to the turbocharger302. The internal wastegate may be utilized in conjunction with or inplace of an external wastegate.

Similarly, as described above, turbocharger 302 includes exhaust turbine308 and compressor 306. Exhaust turbine 308 includes a turbine inlet 310coupled to receive exhaust from first outlet 342 associated with exhaustmanifold 336. Exhaust turbine 308 extracts mechanical energy from thereceived exhaust, which then exits via turbine outlet 312 and iscommunicated to the exhaust muffler. Mechanical energy extracted byexhaust turbine 308 drives the compressor 306 to provide compressed airat compressor outlet 314. As described above, the compressed air isprovided to the two-stroke engine. In some embodiments, the compressedair is provided to the two-stroke engine via a charge air cooler, asshown with respect to FIGS. 17A-18D.

Referring now to FIG. 23, exhaust muffler 324 is shown, which includesexhaust pipe 326 and wastegate exhaust pipe 350. In some embodiments,wastegate exhaust pipe 350 connects to exhaust pipe 326 to provideexhaust exiting wastegate 320 to exhaust pipe 326, which is thenconnected to exhaust muffler 324. In some embodiments, the exhaust pipe(e.g., exhaust pipe 326) connecting the turbocharger to the exhaustmuffler 324 is larger in diameter than the diameter of wastegate exhaustpipe 350. In some embodiments, the mass of exhaust flowing through theturbocharger exceeds—during normal operation—the mass of exhaustexpelled by the external wastegate. In other embodiments, wastegateexhaust pipe 350 may be connected directly to exhaust muffler 324. Insome embodiments, exhaust muffler 324 includes a first inlet forreceiving exhaust from wastegate exhaust pipe 350 and a second inlet forreceiving exhaust from exhaust pipe 326.

Referring now to FIGS. 25A-25D, an exhaust manifold 400 is illustratedaccording to some embodiments, wherein exhaust manifold 400 includesfirst and second exhaust inlets 402 a and 402 b, first and secondoutlets 404 a and 404 b, first and second inlet pipes 406 a, 406 b, andfirst and second outlet pipes 408 a, 408 b. FIG. 25A is a top view, FIG.25B is a perspective view, FIG. 25C is a side view, and FIG. 25D is afront view.

As shown in FIG. 25C, both first and second inlets 402 a, 402 b andfirst and second outlets 404 a, 404 b are located on the same plane. Thetop view of exhaust manifold 400 illustrates the X-shaped geometry ofthe exhaust manifold 400. Exhaust is received at first exhaust inlet 402a and second exhaust inlet 402 b. First and second inlet pipes 406 a and406 b are connected to first and second exhaust inlets 402 a, 402 b,respectively, at a proximal end and connected to one another at a distalend. The connection of first and second inlet pipes 406 a and 406 b atthe distal end allows exhaust from each pipe to mix, wherein the mixedexhaust is bifurcated and provided as an output to first and secondoutlet pipes 408 a and 408 b. A portion of the exhaust provided by firstand second inlets 402 a, 402 b is provided to first outlet 404 a viafirst outlet pipe 408 a, while a portion of the exhaust provided byfirst and second inlets 402 a, 402 b is provided to second outlet 404 bvia second outlet pipe 408 b. In some embodiments, the diameter of thefirst and second inlet pipes 406 a and 406 b are equal to one another.In some embodiments, the diameter of the first and second outlet pipes408 a and 408 b are equal to one another. In other embodiments, thediameter of the first and second outlet pipes 408 a and 408 b are ofdifferent diameter to allow a greater mass of exhaust to flow throughone of the outlet pipes as compared with the other outlet pipe. In someembodiments, first inlet pipe 406 a and second outlet pipe 408 b areapproximately aligned with one another, such that first inlet pipe 406 aand second outlet pipe 408 b share an axis. Likewise, in someembodiments, second inlet pipe 406 b and first outlet pipe 408 a areapproximately aligned with one another, such that second inlet pipe 406b shares an axis with first outlet pipe 408 b.

Referring now to FIGS. 26A-26D, an exhaust manifold 410 is illustratedaccording to some embodiments, wherein exhaust manifold 410 includesfirst and second exhaust inlets 412 a and 412 b, first and secondoutlets 414 a and 414 b, first and second inlet pipes 416 a, 416 b, andfirst and second outlet pipes 418 a, 418 b. FIG. 26A is a top view, FIG.26B is a perspective view, FIG. 26C is a side view, and FIG. 26D is afront view.

In the embodiment shown in FIGS. 26A-26D, first and second inlets 412 aand 412 b are located on the same horizontal plane, and first and secondoutlets 414 a and 414 b are located on the same vertical plane, whereinfirst outlet 414 a is located below second outlet 414 b. In contrastwith the embodiment shown in FIG. 24C, in which first outlet 252 isaligned on the same plane as first and second inlets 250 a and 250 b, inthe embodiment shown in FIGS. 26A-26D first and second outlets 414 a and414 b are offset from the plane defined by first and second inlets 412 aand 412 b. For example, as shown in FIG. 26C, a horizontal plane 420 isprovided that includes both first and second inlets 412 a, 412 b. Afirst axis 422 a is drawn through the center of first outlet pipe 418 aand second axis is drawn through the center of second outlet pipe 418 b.The angle between first axis 422 a and the horizontal plane 420 isillustrated by angle γ₁ and the angle between second axis 422 b and thehorizontal plane 420 is illustrated by angle γ₂. In some embodiments, γ₁is approximately equal to γ₂. In other embodiments, these angles may bemodified to selectively control the flow of exhaust provided to firstand second outlets 414 a and 414 b.

Referring now to FIGS. 27A-27D, an exhaust manifold 420 is illustratedaccording to some embodiments, wherein exhaust manifold 420 includesfirst and second exhaust inlets 422 a and 422 b, and first and secondoutlets 424 a and 424 b. In contrast with embodiments shown in FIGS.25A-25D and 26A-26D in which each exhaust inlet is connected to aseparate inlet pipe, the embodiment shown in FIGS. 27A-27D illustratesbifurcation of the exhaust at each inlet into first and second flows.For example, as shown in FIG. 27B, first inlet 422 a is coupled to firstupper inlet pipe 426 a and first lower inlet pipe 428 a. In this way,exhaust provided from a first cylinder to first inlet 422 a isimmediately bifurcated into first and second exhaust flows. Likewise,second inlet 422 b is coupled to second upper inlet pipe 426 b andsecond lower inlet pipe 428 b, such that exhaust provided from a secondcylinder to second inlet 422 b is immediately bifurcated into first andsecond exhaust flows. Exhaust provided to first upper inlet pipe 426 aand second upper inlet pipe 426 b is combined and provided as an outputto second outlet 424 b. Likewise, exhaust provided to first lower inletpipe 428 a and second lower inlet pipe 428 b is combined and provided asan output to first outlet 424 a. In some embodiments, the diameter offirst and second upper inlet pipes 426 a and 426 b are equal. In someembodiments, the diameter of first and second lower inlet pipes 428 aand 428 b are equal. In some embodiments, the diameter of first andsecond upper inlet pipes 426 a, 426 b is approximately equal to thefirst and second lower inlet pipes 428 a, 428 b. In other embodiments,the diameter of first and second upper inlet pipes 426 a, 426 b isgreater than or less than the diameter of first and second lower inletpipes 428 a, 428 b, depending on the flow requirements of the first andsecond parallel exhaust path.

In some embodiments, first and second inlets 422 a and 422 b are locatedon the same horizontal plane, and first and second outlets 424 a and 424b are located on the same vertical plane, wherein first outlet 424 a islocated below second outlet 424 b. As shown in FIG. 27C, a horizontalplane 430 is provided that includes both first and second, inlets 422 a,422 b. A first plane 432 a is defined to include first and second inlets422 a, 422 b and first outlet 424 a. A second plane 432 b is defined toinclude first and second inlets 422 a, 422 b and first outlet 424 b. Afirst angle defined between horizontal plane 430 and plane 432 a isprovided as α₁ and a second angle defined between horizontal plane 430and plane 432 b is provided as α₂. In some embodiments, α₁ isapproximately equal to α₂ other embodiments, these angles may bemodified to selectively control the flow of exhaust provided to firstand second outlets 424 a and 424 b.

Referring now to FIGS. 28A-28B, a parallel-path exhaust system 520utilized in conjunction with a two-stroke engine 222 are shown. In someembodiments, two-stroke engine 222 includes first and second cylinders.Compressed air provided by the turbocharger 532 and cooled by charge aircooler 538 is provided to the respective cylinders by intake plenum 540.Exhaust generated by the first and second cylinders of two-stroke engine222 is provided to exhaust manifold 524. Various geometries of exhaustmanifold may be utilized, as described above with respect to FIGS.24A-27D. In general, exhaust manifold 524 bifurcates the exhaustprovided by two-stroke engine 222 into first and second parallel paths.In some embodiments, the mass and/or volume of exhaust provided to thefirst and second parallel paths may be equal or unequal, and may changebased on the operating condition of the two-stroke engine. In someembodiments, a first parallel path includes tuned expansion chamber 526,and a second parallel path includes turbocharger 532. As discussedabove, turbocharger 532 includes an exhaust turbine that extractsmechanical energy from the received exhaust, and utilizes the extractedmechanical energy to drive a compressor to provide compressed air to thecharge air cooler 538.

As shown in more detail in FIG. 28B, exhaust manifold 524 includes firstand second inlets 550 a, 550 b connected to receive exhaust from firstand second combustion cylinders, respectively. In addition, exhaustmanifold 524 includes first outlet 552 and second outlet 554, whereinfirst outlet 552 provides exhaust to the first parallel path (e.g., totuned expansion chamber 526) and second outlet 554 provides exhaust tothe second parallel path (e.g., to turbocharger 532).

In some embodiments, tuned expansion chamber 526 includes expansionchamber inlet 574 and expansion chamber outlet 576. In some embodiments,expansion chamber inlet 574 is connected to first outlet 552 of exhaustmanifold 524 to receive exhaust from both the first and secondcylinders. The length and cross-sectional geometry of tuned expansionchamber 526 is selected to reflect wavefronts associated with thereceived exhaust back toward the first and second inlets 550 a, 550 bwith an arrival timed to push any air/gas mixture drawn out of theengine back into the cylinder prior to the port closing before the nextcombustion cycle. In the embodiment shown in FIGS. 28A-28B, tunedexpansion chamber 526 is coupled to first outlet 552. In someembodiments, expansion chamber outlet 576 is coupled to externalwastegate 528 via wastegate inlet 578, which in turn is coupled viawastegate outlet 580 to exhaust pipe inlet 542 associated with exhaustmuffler 530. In this embodiment, exhaust muffler 530 includes separateinlet pipes 542 and 564 for receiving exhaust from the first and secondparallel paths. In particular, inlet pipe 542 is configured forconnection to wastegate outlet 580, and inlet pipe 564 is configured forconnection to exhaust inlet pipe 564, which in turn is connected toturbocharger 532 via exhaust outlet 558. In some embodiments, inlet pipe542 is smaller in diameter than exhaust inlet pipe 564.

Referring now to FIG. 29, a parallel-path exhaust system 620 utilizingboth an external wastegate 638 and an internal wastegate (not visible)is provided. As described above, the parallel-path exhaust system 620includes an exhaust manifold 624, a tuned expansion chamber 626, aturbocharger 632 and an external wastegate 638. In some embodiments, theexhaust manifold 624 includes at least one inlet for receiving exhaustfrom the two-stroke engine. In some embodiments, such as that shown inFIG. 29, the exhaust manifold 624 includes first and second inlets 650 aand 650 b. In addition, exhaust manifold 624 includes first and secondoutlets 652 and 654. Various geometries associated with exhaust manifold624 may be utilized, wherein the position of the exhaust inlets andexhaust outlets are selected to provide the desired bifurcation ofexhaust within the given space constraints of the system.

In some embodiments, tuned expansion chamber 626 includes expansionchamber inlet 674 and expansion chamber outlet 676. In some embodiments,expansion chamber inlet 674 is connected to first outlet 652 of exhaustmanifold 624 to receive exhaust from both the first and secondcylinders. The length and cross-sectional geometry of tuned expansionchamber 626 is selected to reflect wavefronts associated with thereceived exhaust back toward the first and second inlets 650 a, 650 bwith an arrival timed to push any air/gas mixture drawn out of theengine back into the cylinder prior to the port closing before the nextcombustion cycle. In the embodiment shown in FIG. 29, tuned expansionchamber 626 is coupled to first outlet 652. In some embodiments,expansion chamber outlet 676 is coupled to external wastegate 638 viawastegate inlet 678, which in turn is coupled via wastegate outlet 680to the exhaust muffler (not shown). As described above, externalwastegate 638 regulates the exhaust gas within the tuned expansionchamber 626. In some embodiments, external wastegate 638 may be utilizedto regulate the flow of exhaust through the turbocharger 632. However,in the embodiment shown in FIG. 29, turbocharger 632 includes aninternal wastegate (not shown) actuated by internal wastegate actuator640. In some embodiments, external wastegate 638 is utilized to regulatethe flow of exhaust through the tuned expansion chamber 626, and theinternal wastegate associated with turbocharger 632 is utilized toregulate the flow of exhaust through the turbocharger 632. In otherembodiments, the external wastegate 638 and internal wastegate (nowshown) work in unison to control the flow of exhaust through both thetuned expansion chamber 626 and the turbocharger 632.

In some embodiments, turbocharger 632 includes an exhaust inlet 656 forreceiving exhaust from the exhaust manifold (e.g., via exhaust outlet654). Internal wastegate (not shown) provides a path for the receivedexhaust to bypass the turbine portion of the turbocharger 632, therebyreducing the mechanical energy extracted from the received exhaust. Insome embodiments, internal wastegate is controlled or actuated byinternal wastegate actuator 640, which includes pin assembly 644, lever645, and diagram/spring assembly 646. In some embodiments,diagram/spring assembly 646 is configured to actuate lever 645 inresponse to changes in pressure. The actuation of lever 645 causes arotation of pin assembly 644 within opening 642, which is configured toselectively open/close the valve associated with the internal wastegate.In some embodiments, diagram/spring assembly 646 is connected via hose(not shown) to the hose/tube connecting compressed air outlet 660 to thecharge air cooler, such that actuation of the internal wastegate isrelated to the turbo boost pressure. In some embodiments, as turbo boostpressure increases, internal wastegate is actuated to decrease the flowof exhaust through the turbine, and as turbo boost pressure decreases,internal wastegate is actuated to increase the flow of exhaust throughthe turbine. In some embodiments, the turbo boost pressure is alsoutilized as input for controlling external wastegate 638. In someembodiments, a hose (not shown) connected to the hose/tube for providingcompressed air to the charge air cooler provides turbo boost pressureinput to the external wastegate 638. In other embodiments, actuation ofthe valves associated with external wastegate 638 and the internalwastegate (not shown) may be controlled by an engine control unit (ECU)(not shown) based on one or more measured inputs, including one or moreof exhaust pressure, exhaust temperature, exhaust flow through theturbocharger, turbo boost pressure, etc. In this way, internal wastegatemay be pneumatically actuated or electronically actuated, and may bebased on one or more inputs as discussed above.

Referring now to FIG. 30, a tuned expansion chamber 726 is shown thatincludes a fixed flow orifice 728. In some embodiments, tuned expansionchamber 726 includes exhaust inlet 774 and exhaust outlet 730. In someembodiments, exhaust flows through fixed flow orifice 728. The diameterof fixed flow orifice 728 is fixed, and therefore does not act toregulate the flow of exhaust provided by the tuned expansion chamber 726to the exhaust muffler.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. A snowmobile comprising: a frame; at least one ski; handlebarsoperatively coupled to the at least one ski; an engine assemblycomprising an engine and an exhaust manifold, the exhaust manifoldcomprising: at least a first inlet connected to at least a first exhaustport; a first outlet connected to provide exhaust received from thefirst inlet and a second inlet to a first exhaust path; and a secondoutlet connected to provide exhaust received from the first inlet andthe second inlet to a second exhaust path.
 2. The snowmobile of claim 1,wherein the exhaust manifold further includes a second inlet connectedto a second exhaust port, wherein the first inlet, the second inlet, andthe first outlet are oriented in a shared plane and form a Y-shape. 3.The snowmobile of claim 2, wherein the second outlet is oriented at anangle relative to the shared plane defined by the first inlet, thesecond inlet, and the first outlet.
 4. The snowmobile of claim 1,wherein the exhaust manifold further includes a second inlet connectedto a second exhaust port, wherein the first inlet, the second inlet, thefirst outlet, and the second outlet are located on a shared plane andform an X-shape.
 5. The snowmobile of claim 1, wherein the exhaustmanifold further includes a second inlet configured to connect to asecond exhaust port, wherein the first inlet and the second inlet are ona shared plane and the first outlet and the second outlet are on ashared vertical plane.
 6. The snowmobile of claim 5, wherein the firstoutlet is oriented at a first angle relative to the shared horizontalplane defined by the first inlet and the second inlet and wherein thesecond outlet is oriented at a second angle relative to the sharedhorizontal plane defined by the first in let and the second inlet. 7.The snowmobile of claim 6, wherein the first angle is approximatelyequal to the second angle.
 8. A snowmobile comprising: a frame; at leastone ski; handlebars operatively coupled to the at least one ski; anengine assembly comprising an engine and an exhaust manifold, theexhaust manifold having first and second inlets and first and secondoutlets, wherein the first inlet is connected to receive exhaust from afirst cylinder and the second inlet is connected to receive exhaust froma second cylinder, wherein exhaust provided at the first and secondinlets is communicated by the exhaust manifold to the first and secondoutlets; an expansion chamber having a first end connected to receiveexhaust from the first outlet; an external wastegate connected to asecond end of the expansion chamber; and a turbocharger connected toreceive exhaust from the second outlet.
 9. The snowmobile of claim 8,further including: an exhaust muffler connected to receive exhaustoutput from the turbocharger.
 10. The snowmobile of claim 8, wherein theexternal wastegate is actuated in response to one or more of temperaturemeasured within the expansion chamber, exhaust pressure, turbo boostpressure, and flow of exhaust through the turbocharger.
 11. Thesnowmobile of claim 8, wherein the turbocharger includes an internalwastegate to regulate a flow of exhaust through the turbocharger. 12.The snowmobile of claim 8, wherein the first outlet is located above thesecond outlet.
 13. The snowmobile of claim 8, wherein the first outletis located below the second outlet.
 14. The snowmobile of claim 8,wherein the first and second inlets are located on a horizontal plane.15. The snowmobile of claim 8, wherein the first and second inlets andthe first outlet are located on a shared horizontal plane in a Y-shapedconfiguration and the second outlet is oriented at an angle relative tothe shared horizontal plane defined by the first inlet, the secondinlet, and the first outlet.
 16. A snowmobile comprising: a frame; atleast one ski; handlebars operatively coupled to the at least one ski;an engine system comprising: a two-stroke engine having at least a firstcombustion cylinder; an exhaust manifold having at least a first inletand first and second outlets, wherein the first inlet is connected toreceive exhaust from the first combustion cylinder, wherein exhaustprovided at the first inlet is communicated by the exhaust manifold tothe first and second outlets; an expansion chamber having a first endconnected to receive exhaust from the first outlet and a second endconnected to an external wastegate; a turbocharger connected to thesecond outlet to receive exhaust from the exhaust manifold and toutilize the received exhaust to generate compressed air, wherein theexternal wastegate regulates a flow of exhaust through the expansionchamber and through the turbocharger; an exhaust muffler connected toreceive exhaust output from the turbocharger; and an intake manifoldconnected to receive compressed air from the turbocharger and to providethe compressed air to the first combustion cylinder for combustion. 17.The engine system of claim 16, wherein the turbocharger includes aninternal wastegate, wherein the internal wastegate controls a flow ofexhaust through the turbocharger.
 18. The engine system of claim 16,wherein the two-stroke engine includes at least a second combustioncylinder and wherein the exhaust manifold includes at least a secondinlet connected to receive exhaust from the second combustion cylinder,wherein the first and second inlets and the first outlet are located ona shared horizontal plane in a Y-shaped configuration and the secondoutlet is oriented at an angle relative to the shared horizontal planedefined by the first inlet, the second inlet, and the first outlet. 19.The engine system of claim 18, wherein the second outlet is oriented atan angle of less than ninety degrees relative to the shared horizontalplane.